The present invention relates to a gas laser oscillator low in fluctuation rate of a laser beam, capable of producing a laser beam stably, and free from malfunction.
First, a conventional gas laser oscillator is described by referring to FIG. 11. In FIG. 11, reference numeral 1 is a discharge tube for forming a discharge space 5 inside, and the inside of the discharge tube 1 is filled with laser gas, or laser gas is circulating by a circulating device not shown in the drawing. Reference numeral 2 is an electrode provided at one end of the discharge tube 1, 3 is an electrode provided at the other end of the discharge tube 1, 4 is a direct-current high voltage power source for applying a voltage for discharging between the electrodes 2 and 3, and 6 is a fully reflective mirror, which is combined with a partially reflective mirror 7 to compose an optical resonator for amplifying the laser light. Reference numeral 9 is an output control device for controlling the direct-current high voltage power source 4.
This is the basic constitution of the gas laser oscillator. In this constituted gas laser oscillator, the operation of its basic portion is described below. First, according to the command from the output control device 9, a direct-current high voltage in pulse form is applied between the electrodes 2 and 3 from the direct-current high voltage power source 4 for discharging between the electrodes 2 and 3. By this discharge energy, the laser gas in the discharge space 5 is excited. The excited laser gas is set in resonant state by the optical resonator composed of the fully reflective mirror 6 and partially reflective mirror 7, and the light is amplified, and a laser beam 8 is issued from the partially reflective mirror 7. The produced laser beam 8 is used in laser processing such as cutting and piercing.
In such a gas laser oscillator, also on standby while not processing, discharge occurs in the discharge tube 1, and the laser beam 8 is issued from the partially reflective mirror 7 at a preset output level. However, since an absorber 10 is disposed ahead of the partially reflective mirror 7, the produced laser beam 8 is intercepted by the absorber 10 and does not leak outside.
When processing by the laser beam 8, by the command from an absorber control device 12, an absorber drive device 11 operates the absorber 10, and the passage of laser beam 8 is opened, and the laser beam 8 is emitted outside to process the workpiece 15.
On the other hand, at the side closer to the workpiece 15 from the absorber 10 on the optical axis of the laser beam 8, a beam splitter 14 is disposed. The laser beam 8 is separated by this beam splitter 14, and the straightforward portion 8a reaches the workpiece 15, and processes by cutting or piercing. The portion 8b reflected and separated by the beam splitter 14 is focused by a focusing lens 16, and is irradiated onto a detector 17. The detector 17 irradiated by the separated portion 8b detects that the laser beam 8 is being emitted. This detection signal is amplified by an amplifier 18, and is issued from a terminal 19.
However, the conventional gas laser oscillator as explained above had several problems.
First was a problem of fluctuation of laser beam output in a transient state from standby by cutting off the laser beam 8 by the absorber 10 to processing by passing the laser beam 8 by setting aside the absorber 10. That is, in the standby state (A) as shown in FIG. 7, a signal for obtaining an output of low level necessary for maintaining discharge is issued from the output control device 9, and a direct-current high voltage corresponding to the signal level is applied between the electrodes 2 and 3 to maintain discharge. Once a processing start signal is entered and the absorber 10 is opened to be in state (B), the processing start signal 13 is sent from the absorber control device 12 into the output control device 9. Receiving this signal 13, the output control device sends out a signal having a level and waveform necessary for obtaining the output of pulse laser beam 8 suited to the purpose of processing. In the conventional control, however, since the discharge state in the discharge space 5 on standby is different from the discharge state in the discharge space 5 during processing, the dissociation state of laser gas is different between processing and standby. As a result it takes time until the dissociation state of laser gas is stabilized from start of processing and fluctuations of laser output in the initial period of processing are large so that stable processing is disabled. Upon start of processing, further, it takes time to stabilize owing to the presence of an unstable period due to heat effects of the fully reflective mirror 6 and partially reflective mirror 7 for composing the optical resonator and unstable period of surface state of the electrode 2 and electrode 3, which is also a cause of an unstable output of the laser beam 8 in the initial period of processing. This unstable output of the laser beam 8 in the initial period of processing was a serious problem in processing for a short time, in particular.
Another problem is related to the laser beam detecting device that is indispensable for accurate control of the gas laser oscillator. In the conventional constitution shown in FIG. 11, after dismounting the beam splitter 14 for the purpose of an adjustment of the gas laser oscillator or the like, if laser processing is done without reassembling the beam splitter 14, the laser beam 8 not attenuated by the beam splitter 14 directly irradiates to the workpiece 15. As a result, the workpiece is irradiated with an excessive laser beam 8, and a processing failure may occur.
Also, there is a possibility that when adjusting the gas laser oscillator, if a laser beam 8 over the allowable capacity of the detector 17 is irradiated by mistake, the detector 17 may be broken.
Further, the detector 17 may fluctuate in the detecting sensitivity due to fluctuations of temperature depending on heat generation by incident of laser beam 8b or ambient temperature. A fluctuation of detecting sensitivity of the detector 17 may cause output of wrong information. For example, if the detecting sensitivity is raised, although the laser beam 8 is not emitted, it may be falsely recognized that the laser beam 8 is emitted, or if the detecting sensitivity is lowered, although the laser beam 8 is emitted, it may be falsely recognized that the laser beam 8 is not emitted. Hence, accurate control of the gas laser oscillator may be disabled.
Moreover, if used for a long period, dust may deposit on the beam splitter 14, focusing lens 16, or detecting surface of the detector 17, and the detecting sensitivity may be lowered.
The invention is hence devised to solve the above plural problems, and it is a first object thereof to transfer promptly to a state of stable and favorable laser processing by eliminating the unstable period of laser beam output in the transient state of changing from standby to processing.
It is a second object to solve the problems relating to the laser beam detector, including prevention of processing failure by irradiation of laser beam of excessive energy to the workpiece if forgetting to mount the beam splitter, prevention of damage of the detector due to excessive input to the detector by wrong adjustment, and prevention of wrong control of gas laser oscillator due to malfunction of detector caused by fluctuations of detector temperature or deposit of dust.
To achieve the objects, the gas laser oscillator of embodiment 1 of the invention comprises:
a discharge tube for forming a discharge space inside,
a fully reflective mirror disposed toward the opening at one end of the discharge space for composing an end mirror,
a partially reflective mirror disposed toward the opening at the other end of the discharge space for composing an output mirror,
a pair of electrodes disposed at both ends of the discharge tube,
a direct-current high voltage power source for discharging in the discharge space by applying a high voltage of pulse form between the pair of electrodes,
an output control device for controlling the output of the direct-current high voltage power source,
a movable absorber disposed outside of the partially reflective mirror for opening and closing the passage the of laser beam,
a drive device for driving to open or close the absorber, and
an absorber control device for controlling the drive device so as to move the absorber to a position for intercepting the laser beam on standby, and to move to a position so that the absorber may not interfere passing of laser beam during processing,
in which the output control device controls the direct-current high voltage power source so as to discharge in the same condition both upon standby and during processing.
The gas laser oscillator of embodiment 2 of the invention comprises:
a discharge tube for forming a discharge space inside,
a fully reflective mirror disposed toward the opening at one end of the discharge space for composing an end mirror,
a partially reflective mirror disposed toward the opening at the other end of the discharge space for composing an output mirror,
a pair of electrodes disposed at both ends of the discharge tube,
a direct-current high voltage power source for discharging in the discharge space by applying a high voltage of pulse form between the pair of electrodes,
an output control device for controlling the output of the direct-current high voltage power source,
a beam splitter disposed outside of the partially reflective mirror so as to cut across the passage of laser beam for separating the laser beam,
a switch which is actuated when the beam splitter is installed at a specified position,
a focusing lens for focusing the laser beam separated by reflection by the beam splitter,
a detector for detecting the laser beam focused by the focusing lens,
an amplifier for amplifying the output of the detector and issuing a signal to the output control device,
a shielding plate disposed between the focusing lens and detector for opening and closing, and
a switch which is actuated when the shielding plate is opened.
In the gas laser oscillator of embodiment 2, preferably, the output control device controls the direct-current high voltage power source so that the laser beam may be emitted only while the switch which is actuated when the beam splitter is installed at a specified position is being actuated.
In the gas laser oscillator of embodiment 2, preferably, the output control device controls the direct-current high voltage power source so as not to emit a laser beam exceeding the maximum allowable input of the detector while the switch which is actuated when the shielding plate is opened is being actuated.
In the gas laser oscillator of embodiment 2, preferably, the detector is provided with a passage of a medium so as to exchange heat with the medium, and the detector is controlled of temperature by the medium controlled of temperature.
In the gas laser oscillator of embodiment 2, preferably, the beam splitter, the focusing lens, and the detector are disposed so that the axis of laser beam passing therethrough may be in the horizontal direction.
According to the gas laser oscillator of embodiment 1, it is controlled so as to emit laser beam of a same pulse width and a same pulse frequency at a same output level whether on standby or during processing, and the laser beam is prevented from escaping outside by the absorber, and therefore, on standby, the dissociation state of the laser gas is the same as during processing, and it does not take time to stabilize the dissociation state upon start of processing. Moreover, the temperature of the partially reflective mirror and the fully reflective mirror and surface state of the electrodes are the same on standby and during processing, and a transient unstable state does not occur upon start of processing, and the laser output is not unstable in the initial period of processing, so that favorable laser processing may be done.
According to the gas laser oscillator of embodiment 2, the laser is not produced unless the beam splitter is installed at a specified position, and therefore the workpiece is not irradiated with laser beam not attenuated by the beam splitter, and processing failure due to an application of excessive input to the workpiece is avoided. Moreover, while the shielding plate is open, it is controlled so as not to emit the laser beam exceeding the maximum allowable input of the detector, and the detector is not broken by excessive input. Moreover, since the detector is controlled of temperature by the medium controlled of temperature, the temperature of the detector is not changed by the input of laser beam or ambient temperature, and a stable detecting sensitivity is obtained. Moreover, since the beam splitter, focusing lens and detector are installed so that the optical axis of the laser beam passing through the beam splitter, focusing lens and detector may be horizontal, deposit of dust on the reflecting surface of the beam splitter, surface of the focusing lens, and detecting surface of the detector is lessened, reduction of the sensitivity of the detector in the time course are improved notably, and a stable detecting sensitivity is obtained for a long period.